import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution5 {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param lists ListNode类ArrayList 
     * @return ListNode类
     */
    public ListNode mergeKLists (ArrayList<ListNode> lists) {
        // write code here
        if(lists.size() == 0){
            return null;
        }        
        ListNode root = fun(lists, 0, lists.size()-1);
        return root;        
    }
    public ListNode fun(ArrayList<ListNode> lists, int left, int right){
        if(left >= right){
            return lists.get(left);
        }
        int mid = (left + right) / 2;
        ListNode Left = fun(lists,left, mid);
        ListNode Right = fun(lists,mid+1, right);
        return merge(Left, Right);
    }
    public ListNode merge(ListNode head1, ListNode head2){
        ListNode root = new ListNode(0);
        ListNode cur = root;
        while(head1 != null && head2 != null){
            if(head1.val < head2.val){
                cur.next = head1;
                head1 = head1.next;
            } else {
                cur.next = head2;
                head2 = head2.next;
            }
            cur = cur.next;
        }
        if(head1 != null){
            cur.next = head1;
        }
        if(head2 != null){
            cur.next = head2;
        }
        return root.next;
    }
}